Ambulatory Electrocardiographic Monitor For Providing Ease Of Use In Women And Method Of Use

ABSTRACT

A method for performing ambulatory electrocardiographic monitoring on an adult female is provided. An ambulatory ECG monitor, that includes a plurality of sensing electrodes coupled to self-powered sensing circuitry, is provisioned. A monitoring site is located on the surface of a patient&#39;s chest at midline and above the body of the sternum adjacent to the fourth and fifth intercostal spaces between the breasts in the upper portion of the intermammary cleft. The electrodes are aligned and placed along the midline. Interference from breast tissue with placement of the ambulatory monitor at the monitoring site is evaluated. The ambulatory ECG monitor is removably adhered to the monitoring site clear of any breast tissue interference for the duration of monitoring. ECG data is sensed through the sensing electrodes at the monitoring site and the sensed ECG data is recorded into the sensing circuitry.

FIELD

This application relates in general to ambulatory electrocardiographyand, in particular, to an ambulatory electrocardiographic monitor forproviding ease of use in women and method of use.

BACKGROUND

The cardiac electrical signal begins in the cells of the sinoatrial nodein the right atrium. These cells spontaneously depolarize and create acardiac action potential of electrical impulses that rapidly propagatesoutward across the right atrium and then the left atrium. The cardiacaction potential in turn stimulates muscle cells of the atrialmyocardium to depolarize and contract to push blood into the ventricles.Shortly thereafter, this atrial action potential encounters theatrioventricular node located at the juncture of the atria andventricles near the center of the heart. The atrioventricular nodeslightly delays cardiac action potential propagation into the ventriclesto ensure complete drainage of blood from the atria. Thereafter, themuscle cells of the ventricular myocardium are activated by theelectrical wave front and are stimulated into systolic contraction.After a rest and reset period, the complete the heart beat cyclerepeats. Any disruption in this process, which can include heart block,sinus bradycardia, atrial fibrillation, and ventricular tachycardia, canlead to the symptoms ranging from dizziness to a sensation of heartfluttering or palpitations, loss of consciousness or even death. Beingable to record the electrical signal of the heart is a fundamentaldiagnostic tool of every physician.

Identifying abnormal rhythms depends upon the manner in which and theamplitude of the depolarization signal of the muscle cells of the atrialand ventricular myocardium that in turn act as sequential voltagesources, which generate a current flow across the thoracic region of thebody and result in a characteristic signal on the body surface. In atypical electrocardiographic (ECG) monitor, cardiac action potentialsoccur between 0.05 Hz to 150 Hz with a signal strength of around 3mVp-p(peak-to-peak). Although miniscule, the current flow can be measured tocharacterize the electrical activity of the heart using an ECG monitoror similar device. Voltage differentials from pairings of the electrodesare filtered, amplified, and combined into P, QRS, and T complexes.

Conventionally, cardiac action potentials are detected throughelectrodes attached to the skin on the chest and limbs based on theAmerican Heart Association's classic 12-lead placement model, such as P.Libby et al., “Braunwald's Heart Disease—A Textbook of CardiovascularMedicine,” Chs. 11 and 12 (8^(th) ed. 2008), the disclosure of which isincorporated by reference. Both traditional in-clinic and ambulatoryHolter-style ECG monitors follow the standard 12-lead model withvariations on numbers and placement of leads. Generally, limb leadelectrodes are placed on each arm and on the left leg, while precordiallead electrodes are placed on the left upper chest region over the heartin close proximity to the heart and at a location of strongest cardiacaction potential signal strength. In turn, the monitoring circuitryrelies on the superior signal strength from over-the-heart electrodeplacement and the relatively long signal vector length that is affordedby lead placement over a wider physical expanse of the body. Forinstance, based upon the large inter-electrode distances, signalamplification assumes a signal strength of around 3mVp-p (peak-to-peak).The limb leads can be re-positioned as necessary to compensate forvariability in patient anatomy due to tissue and bone density and heartposition.

The 12-lead placement model, however, is poorly suited to long-termambulatory monitoring both from the perspective of comfort and from theperspective of reliability, particularly in adult women, as well as onother patients with large-girthed, fatty, or well-developed upper chestregions. The latter concern simply relates to how standard monitoringelectrodes fall off with modest movement, as well as how signal qualitydiminishes when electrodes are placed over breast tissue, as isunavoidable in some women. In-clinic ECG monitoring, for instance,assumes that the patient will remain relatively stationary and that thelimb leads can be repositioned as necessary to provide sufficientelectrode separation for recording a signal of reasonable amplitude andto compensate for variability in patient anatomy. In contrast, duringambulatory monitoring, a woman's body is in continual motion, evenduring sleep, albeit to a lesser degree. Electrodes are apt to detachand signal quality degrades or is absent altogether. Additionally, inwomen, changes in body position, for instance, lying down, stretching,or bending over, can displace the positioning of the breasts and thecorresponding changes in tissue and bone density can deleteriouslyaffect any electrodes placed thereon. Breasts also exhibit pendulousmotion in proportion to overall size in response to motor activities,such as walking, running, biking, or exercise. Such recurrent motion canact to progressively detach items adhered to the soft tissues, like thebreasts, and are likely to irritate the skin when motion leads toelectrode patch tension. Moreover, breast tissue can increases thedistance between sensing electrodes placed and the underlying heart.Breast tissue may also force placement of the electrode in a suboptimallocation for recording the cardiac signal to remain comfortable,especially during long-term monitoring. The trade-off in women,especially active or large breasted, buxom women, can account for poorECG signal quality.

Holter and other forms of ambulatory ECG monitors generally rely onelectrodes placed close to the heart as suggested by the 12-leadplacement model. For instance, U.S. Pat. No. 3,215,136 issued Nov. 2,1965 to Holter et al. discloses an electrocardiographic recording andplayback means. Episodes of ventricular tachycardia, asystolicintervals, and ectopic heart activities are sensed by electrodesdisposed on the patient's skin in a suitable location, with sufficientinter-electrode separation. These signals are ordinarily recorded via acompact recorder worn by the patient that records an electrocardiogram(ECG) while he engages in activities of daily living, which subsequentlyallows a cardiac specialist to temporally correlate patient symptoms andcardiac abnormalities with activities. A cardiac rhythm disorder, aswell as the absence of a rhythm disorder during symptoms, can sometimesbe identified by having the patient record those symptoms during the useof the Holter monitor.

U.S. Pat. No. 6,117,077 issued Sep. 12, 2000 to Del Mar et al. disclosesa long-term ambulatory physiological recorder provided in a relativelyplanar and triangular-shaped recorder housing with three adhesiveelectrode pads. The recorder is fully self-contained and mountedimmediately adjacent to the organ system that is to be monitored.Electrode pads are adhesively and conductively attached to the patient'sleft chest in a position generally over the heart with positive andnegative terminals in a relative vertical position from the top to thebottom of the heart. Additional electrode leads can also be connected toan input port on the recorder and placed over adjacent areas of theupper chest.

U.S. Pat. No. 6,456,872 issued Sep. 24, 2002 to Faisandier discloses aHolter-type apparatus for recording physiological signals indicative ofcardiac activity. A base unit is formed of a flexible sheet carryingelectrodes and a recording case that carries a battery and flexibleprinted circuit material. The base unit is disposable and can be changedwith each new patient examination. The recorder case is fixed inposition on the patient's thorax through a plurality of electrodesaffixed either through adhesion or through depression using suctioncups. Alternatively, the base unit can be carried by a thoracic belt ora hanging strap collar. The recording case includes electronic circuitsfor the collection and processing of ECG signals and a data transmissionport is provided for by-directional exchange of data, controlparameters, and information.

U.S. Pat. No. 7,257,438 issued Aug. 14, 2007 to Kinast discloses apatient-worn medical monitoring device that includes a lanyard andelectronics package supported in the manner of a pendant. A lanyardincludes integral electrodes or other sensors for making physiologicalmeasurements, which may be stored in a monitor for later readout ortransmitted, before or after processing, to a remote location. Thedevice can locally process and analyze a patient's signals and transmitonly summary data or analyzed results to a remote device.

Finally, U.S. Patent application, Publication No. 2007/0255153, filedNov. 1, 2007, to Kumar et al.; U.S. Patent application, Publication No.2007/0225611, filed Feb. 6, 2007, to Kumar et al.; and U.S. Patentapplication, Publication No. 2007/0249946, filed Feb. 6, 2007, to Kumaret al. disclose discloses a non-invasive cardiac monitor and methods ofusing continuously recorded cardiac data. A heart monitor suitable foruse in primary care includes a self-contained and sealed housing. Thehousing encloses an electronic memory connected to electrodes on theupper left chest to detect an ECG. A thin, flexible, and tapered rim orlip is provided around the edges of the electronics portion of themonitor to increase the surface area available for adhesion.Continuously recorded cardiac monitoring is provided through a sequenceof simple detect-store-offload operations that are performed by a statemachine. The housing is adapted to remain affixed to a patient for atleast seven days. The heart monitor can include an activation or eventnotation button, the actuation of which increases the fidelity of theECG information stored in the memory. The stored information can beretrieved and analyzed offline to identify both normal and abnormal ECGevents. The monitor is specifically intended to provide monitoringcontinuously and without interruption over an extended period. Despitethe improvement in size and case of use of such a system, neither thisdevice or any of the above described systems defines a device capable ofextremely simple and reliable application for any body habitus and byany individual regardless of training. The application of this monitoris especially problematic for large breasted, buxom women.

Finally, U.S. Patent application, Publication No. 2008/0284599, filedApr. 28, 2006, to Zdeblick et al. and U.S. Patent application,Publication No. 2008/0306359, filed Dec. 11, 2008, to Zdeblick et al.,disclose a pharma-informatics system for detecting the actual physicaldelivery of a pharmaceutical agent into a body. An integrated circuit issurrounded by pharmacologically active or inert materials to form apill, which dissolve in the stomach through a combination of mechanicalaction and stomach fluids. As the pill dissolves, areas of theintegrated circuit become exposed and power is supplied to the circuit,which begins to operate and transmit a signal that may indicate thetype. A signal detection receiver can be positioned as an externaldevice worn outside the body with one or more electrodes attached to theskin at different locations. The receiver can include the capability toprovide both pharmaceutical ingestion reporting and psychologicalsensing in a form that can be transmitted to a remote location, such asa clinician or central monitoring agency.

Therefore, a need remains for an ambulatory ECG monitoring device andmethod of use adapted to long term monitoring that resists body movementwhile providing ease and discreteness of use and patient comfortregardless of patient knowledge and regardless of patient body habitus.

SUMMARY

A small and anatomically adaptive ambulatory electrocardiogram monitorincludes a disposable ECG monitor that is applied in-clinic by a primarycare provider, by the patient at home, or by other healthcare or layindividuals to record ECG data over an extended time period while thepatient engages in activities of daily living. The shape of the ECGmonitor is adapted to placement on women and large-chested individuals.The patient's upper thoracic region is evaluated, including determiningwhat affect breast physiology will have on extended placement of the ECGmonitor. The ECG monitor is placed on the patient's chest at midline inthe upper portion of the intermammary cleft, covering the center thirdof the sternum and centered between the manubrium and the xiphoidprocess on the inferior border of the sternum. This unique location forECG monitor application and the monitor's small size allow for auniformity of applicability by minimally trained physicians or even layindividuals. Upon completion of monitoring, the patient delivers thedisposable monitor to a reading service, along with encoded patientmedical information and a diary recording the patient's subjectiveimpressions contemporaneous to the monitoring, such as described incommonly-assigned U.S. patent application, entitled“Computer-Implemented System And Method For Evaluating AmbulatoryElectrocardiographic Monitoring of Cardiac Rhythm Disorders,” Ser. No.______, filed Oct. 8, 2010, pending, the disclosure of which isincorporated by reference. A unique identifier assigned to thedisposable monitor is also provided with the sealable envelope. Thereading service interprets the ECG data and patient medical informationand, where indications of a cardiac rhythm disorder or other healthconcern arise, an automated referral to a cardiac specialist, or otherhealthcare specialist, is made. The patient and his primary careprovider are also informed.

One embodiment provides a method for performing ambulatoryelectrocardiographic monitoring on an adult female is provided. Anambulatory ECG monitor, that includes a plurality of sensing electrodescoupled to self-powered sensing circuitry, is provisioned. A monitoringsite is located on the surface of a patient's chest at the sternalmidline adjacent to the fourth and fifth intercostal spaces between thebreasts in the upper portion of the intermammary cleft. The electrodesare aligned and placed along the midline. Interference from breasttissue with placement of the ambulatory monitor at the monitoring siteis evaluated. The ambulatory ECG monitor is removably adhered to themonitoring site clear of any breast tissue interference for the durationof monitoring. ECG data is sensed through the sensing electrodes at themonitoring site and the sensed ECG data is recorded into the sensingcircuitry.

A further embodiment provides a method for performing ambulatory ECGmonitoring at a midline sternum-centered location of an adult female. Anambulatory ECG monitor, that includes a plurality of sensing electrodescoupled to self-powered sensing circuitry and enclosed in a flexiblehousing, is provisioned. The flexibility of the housing is integral tothe design to comfortably adhere to the sternal surface. The sternalsurface is non-planar, even in men, and the surface of the skin over thesternum has a subtle three-dimensional topography. A properunderstanding of this topography is critical to device design, asprovided through the shape and flexibility of the housing, to ensurethat ECGs can be recorded from the sternal location in women. A layer ofskin adhesive is independently suspended from a bottom of the flexiblehousing. A monitoring site is located on the surface of a patient'schest at midline and adjacent to the fourth and fifth intercostal spacesbetween the breasts in the upper portion of the intermammary cleft, alocation ideal for recording both atrial and ventricular cardiacsignals. Interference from breast tissue with placement of theambulatory monitor at the monitoring site is evaluated. The ambulatoryECG monitor, due to its specific tapered and elongated triangulatedshape with rounded edges, is conformably placed in this location, evenin the face of significant cleavage. The electrodes are aligned andplaced along the midline. The skin adhesive is removably adhered to themonitoring site to avoid the breast tissue interference. The housing isaxially and laterally bendable along the non-planar contours of themonitoring site. ECG data is sensed through the sensing electrodes atthe monitoring site and the sensed ECG data is recorded into the sensingcircuitry.

A still further embodiment provides a ambulatory electrocardiographic(ECG) monitor for an adult woman. Self-powered ECG sensing circuitry isprovided. A plurality of sensing electrodes are coupled to the sensingcircuitry. A housing encloses the sensing circuitry. A skin adhesivelayer facing a contact surface and independently suspended from thehousing with a set of standoffs having non-uniform heights is affixed toand defines an increasingly wide gap between the skin adhesive layer anda bottom surface of the housing.

A yet even further embodiment provides ambulatory electrocardiographic(ECG) monitor with conformal shape and independent suspension for anadult woman. A flexible ECG circuitry body includes self-powered ECGsensing circuitry including a processor, memory, and finite powersupply, a circuit board exhibiting axial and lateral flexibility andupon which the sensing circuitry is included, and a housing enclosingthe circuit board. A plurality of sensing electrodes are coupled to theprocessor, which processes and stores sensed ECG data into the memory. Askin adhesion assembly includes a layer of skin adhesive facing acontact surface, and a set of standoffs having non-uniform heightsaffixed to and defining an increasingly wide gap between the skinadhesive layer and a bottom surface of the housing of the circuitrybody.

An ambulatory ECG monitor in accordance with foregoing embodiments canbe built at low cost, size and weight with a bill of materials of aboutone fifth of the cost of a conventional ambulatory ECG monitor. Low costenables clinics and hospitals to maintain amble inventory at all times,thereby facilitating the ebb and flow of patients in need of ambulatoryECG monitoring who will not need to wait on monitor availability orlaboratory staffing for use and overread.

Additionally a single-use ECG monitor in the form of an adhesive patchin accordance with foregoing embodiments can be constructed with aweight of less than two ounces and inter-electrode spacing of less than6 cm, which presents three advantages. First, costs for shipping themonitors to clinics, hospitals, pharmacies, and other locations arereduced, especially when large quantities must be mailed around theworld. Second, small size and weight ambulatory ECG monitors can beeasily carried in the pockets of health care providers and thereforeapplied upon demand without the need to either retrieve the monitorsfrom a special location or to send the patient to a separate laboratory.Third, small, lightweight ambulatory ECG monitors reduce shear forces onthe skin, which further ensures good signal acquisition and long-termECG recording by facilitating adherence to the skin and comfort for thepatient.

Still other embodiments will become readily apparent to those skilled inthe art from the following detailed description, wherein are describedembodiments by way of illustrating the best mode contemplated. As willbe realized, other and different embodiments are possible and theembodiments' several details are capable of modifications in variousobvious respects, all without departing from their spirit and the scope.Accordingly, the drawings and detailed description are to be regarded asillustrative in nature and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front anatomical diagram showing placement of an ambulatoryelectrocardiographic monitor on a female patient.

FIG. 2 is a cutaway anatomical diagram showing placement of theambulatory electrocardiographic monitor of FIG. 1.

FIG. 3 is an exploded perspective view of an ambulatoryelectrocardiographic monitor in accordance with one embodiment.

FIG. 4 is a side view of the ambulatory electrocardiographic monitor ofFIG. 3.

FIG. 5 is a bottom view of the ambulatory electrocardiographic monitorof FIG. 3.

FIG. 6 is an exploded side view of the ambulatory electrocardiographicmonitor of FIG. 3.

FIG. 7 is a functional block diagram showing the groups of electroniccomponent of the ambulatory electrocardiographic monitor of FIG. 3.

DETAILED DESCRIPTION

Ambulatory ECG monitoring can be improved by locating the leadelectrodes to body positions better adapted to minimize artifacts due tobody movement. FIG. 1 is a front anatomical diagram 10 showing placementof an ambulatory electrocardiographic (ECG) monitor 11 on an adultfemale patient 12. Placement of the monitor 11 on an adult femalepatient 12 can require additional considerations to ensure safety,comfort, and long-term adhesion over the course of the monitoringperiod. The same considerations may apply on non-adult female patientswith large-girthed, fatty, or well-developed breasts to whom the presentdiscussion is primarily focused. For clarity, the term “female” willapply to individuals in this entire class of patients without regard toage or gender or other physical characteristics or traits not germane tothe selection of the monitoring site and placement of a monitor 11 onthe patient's chest.

For these kinds of patients, the monitor 11 is placed between thebreasts 14 a, 14 b in the upper portion of the intermammary cleft 15.The breast size, shape, position, symmetry, overall body physique,posture, and other factors, such as the type of brassiere worn and itsfit or the presence of artificial implants are carefully evaluatedrelative to the size of the monitor 11 for ensuring that the monitor 11does not overlap with, sit or press upon, and otherwise significantlyinterfere with the natural movement and positioning of the breasts 14 a,14 b. The placement of the monitor 11 depends upon the width, length,depth, and relative location of the intermammary cleft 15. A skinadhesion layer of the monitor 11 is firmly adhered within the upperintermammary cleft 15 with the assembly housing the ECG recordingcircuitry bending in conformity to the shape of the sternum and beingindependently suspended above the skin adhesion layer to resisttorsional body movement, as further described infra.

The monitor 11 may be applied in-clinic by a primary care provider, orby the patient herself, for instance, under a physician's orders afterfirst obtaining the monitor 11 from a pharmacy or other authorizeddispensary, such as described in commonly-assigned U.S. patentapplication, entitled “Computer-Implemented System and Method forMediating Patient-Initiated Physiological Monitoring under ConsolidatedPhysician Supervision,” Ser. No. ______, filed Oct. 8, 2010, pending,the disclosure of which is incorporated by reference. The monitor 11 istypically used over a 24-48 hour period, but the monitoring period couldbe extended from seven days up to 30 days through use of a series ofmonitors. During monitoring, the patient 12 engages in activities ofdaily living, while the monitor 11 unobtrusively monitors and collectsECG data. Recording commences upon physical application of the monitor11 and ends when the monitor 11 is removed, typically by the patient 12.Along with the monitor 11, the patient 12 receives instructions forhaving the monitor 11 processed post-monitoring, which can be performedby a reading service, such as described in commonly-assigned U.S. patentapplication, entitled “Computer-Implemented System And Method ForEvaluating Ambulatory Electrocardiographic Monitoring of Cardiac RhythmDisorders,” cited supra. As appropriate, the patient 12 is referred to amedical specialist for follow up care, such as described incommonly-assigned U.S. patent application, entitled“Computer-Implemented System and Method for Facilitating PatientAdvocacy through Online Healthcare Provisioning,” Ser. No. ______, filedOct. 8, 2010, pending, the disclosure of which is incorporated byreference.

Proper placement of the monitor 11 is critical to recording high qualityECG data. FIG. 2 is a cutaway anatomical diagram 20 showing placement ofthe ambulatory electrocardiographic monitor 11 of FIG. 1. The ambulatorymonitor 11 is removably adhered onto the skin on the patient's chest 21at midline, covering the center third of the chest 21 over the sternum26, roughly between the third and fifth ribs 25 a, 25 b andapproximately centered between the suprasternal notch 23 on the superiorborder of the manubrium and the xiphoid process 24 on the inferiorborder of the sternum 26.

The midline sternum-centered monitoring site enables high P-wave andQRS-wave acquisition and provides several additional benefits over othermore typical cutaneous monitoring locations like those locations overthe left upper chest or in the left inframammary crease. First,electrical current originating from the atria and ventricles flowdirectly underneath the sternum 26 providing excellent P waves and QRSwaves necessary for cardiac rhythm diagnosis. Signal quality is furtherimproved by minimizing the depth of tissue, and noise thus generated bymoving tissue, between the monitor's electrodes and the heart. Tissuedepth is fairly consistent at the sternal midline where variations inthe patient's weight and physical topology least interfere with ECGsignal pickup. The midline sternum-centered location enables themonitor's electrodes to record an ECG of optimal signal quality from alocation immediately above the strongest signal-generating aspects ofthe heart. Further, the surface of the skin located over the midlinesternum-centered location remains relatively stationary, despite bodymotion or movement of underlying breast tissue 29, as well as muscle orother body tissue. Movement of the skin surfaces of the upper thoracicregion can be of significant moment, particularly on obese patients orwomen with large or heavy breasts. Adhering the monitor 11 to a bodyposition of minimal movement helps ensure that the monitor 11 remainsadhered to the patient 12 throughout the entire monitoring period, asfurther described infra.

The ambulatory ECG monitor is constructed to provide low cost widespreaduse, with a particular emphasis in improving patient care at the primarycare medical practice level, especially for women. FIG. 3 is an explodedperspective view 40 of an ambulatory electrocardiographic monitor 41 inaccordance with one embodiment. Physically, when viewed from above, themonitor 41 has an elongated triangular shape with rounded vertices, suchas described in commonly-assigned U.S. Design Patent application,entitled “Ambulatory Electrocardiographic Monitor,” Ser. No. ______,filed Oct. 8, 2010, pending; the disclosure of which is incorporated byreference, with dimension's of approximately 3.8 cm (1.5 in) wide and7.6 cm (3.0 in) long with a pair of electrodes 48 spaced less than 6 cmapart. The monitor 41 weighs about 14.2 g (0.5 oz) when assembled withelectrodes 48 and a waterproof housing for the ECG recording circuitry,although a weight of up to 28 g (1.0 oz) would be acceptable. In oneembodiment, the pair of electrodes 48 have an approximately 5.33 cmspacing, although other electrode spacing, generally less than 6 cm, andcombinations of three or more electrodes could also be used. Whenadhered onto a patient's sternum, the narrowest part of the monitor 41faces downwards towards the patient's feet. On a female patient, thenarrow part fits partway into the upper intermammary cleft 15. The smalland narrow size, as well as the taper, allow the monitor 41 to fitcomfortably between the breasts.

The monitor 41 is constructed in a modular fashion and includes aflexible housing and standoff-separated skin adhesion assembly. Thehousing includes a cover 42, printed circuit board (PCB) 43, and coverbase 44, and the skin adhesion assembly includes a set of standoffs 45a, 45 b, a layer of skin adhesive 46, and a set of electrodes 48. Thehousing protects the electronic components for sensing and recording ECGdata, as further described below with reference to FIG. 7, which areaffixed to the PCB 43. The cover 42 conformably fits against the edgesof the cover base 44. The cover 42 and cover base 44 form a waterresistant enclosure that fully enclose the PCB 43. In a furtherembodiment, the housing 61 is vented, which allows the cover 42 toslightly “give” when pressed. A button 47 is formed on the top surfaceof the cover 42 that engages a switch on the PCB 43, which the patientcan press during monitoring to mark an event occurrence, such as onsetof dyspnea. An indicator light 49, such as a light emitting diode,visually signals the patient 12 that the monitor 11 is working. A steadylight signifies normal operation, while a blinking light indicates aproblem.

The outer materials are selected for extended term use. The cover 42 andcover base 44 are both constructed from flexible bio-safe materials,such as plastic, silicon, or foam, and can be vacuum-formed, extruded,or die cut. The adhesive layer 46 is constructed using an adhesivefabric or cloth, which can be woven, as well as latex, foam, and othermaterials that sufficiently resist the twisting and torquing of theskin's surface. In a further embodiment, darts are cut into theperiphery of the adhesive layer 46 to more closely conform the adhesivelayer 46 to an uneven or contoured skin surface. Other materials andmethods of manufacture are possible.

The housing and skin adhesion assembly facilitate long term monitoring.Continuous and uninterrupted wear of the monitor 41 over the entirecourse of monitoring may be impracticable for every patient. Skinsensitivities, allergies, irritation, and similar factors have an effecton a patient's ability to tolerate the wearing of the monitor 41 for anextended period. Similarly, oil on the skin's surface, perspiration, andoverall physical hygiene can affect monitor adhesion. As a result, thehousing can be separated from the skin adhesion assembly to allow thepatient 12 to reposition or replace the skin adhesion assembly. The setof electrodes 48 fit within set of standoffs 45 a, 45 b and a set ofholes or “gel wells,” in the skin adhesive layer 46. In turn, the skinadhesive layer 46 is affixed to the cover base 44 through a combinationof a pair of snap-on or similar form of removable connectors facingdownwardly from the PCB 44 and adhesive applied to the upward facingsurfaces of the standoffs 45 a, 45 b.

To facilitate overall long term monitoring through a series of shortterm monitoring periods, the housing can be separated from the skinadhesion layer and either a new skin adhesion layer can be applied, orthe existing skin adhesion layer can be repositioned. Either the samehousing or a new housing can be used during successive periods ofmonitoring. When the same housing is reused, the recording circuitrycompensates for disconnection and reconnection of the sensing electrodesby stopping recording of ECG data during the gap in monitoring, assensed by disconnection from the set of electrodes 48. The recordingcircuitry thereafter resumes recording upon being reconnected to a setof electrodes 48. If necessary, the patient 12 may choose to take abreak and allow her skin to “breathe” between applications of the skinadhesion layer.

In one embodiment, the monitoring circuit for ECG recording used by themonitor 10 operates under microprogrammed control on a single channel ofanalog input signals. The signals originate as cardiac action potentialssensed from the skin's surface by a single sensing electrode pair,although multiple sensing electrode pairs could be employed withmodifications to the monitoring circuit to factor in multiple inputsignal channels. The analog input signals are converted into digitizedform and encoded for efficient compressed data storage in non-volatilememory. The monitoring circuit injects a reference feedback signal intoboth the analog input signal path and the patient's body. Thus, noisegenerated by the electronics is integrated into the input signals,rather than being filtered or rejected. The monitoring circuit isthereby able to operate unshielded, with no filtering, and throughminimal power filtering components, which thereby eliminates the needfor either the cover 42 or cover base 44 to include physical noiseshielding is eliminated through unique printed circuit board design andlayout, as well as careful selection of electronic components thatnaturally dampen received noise. As well, the digitization andcompression of the original low noise analog signal requires less memoryto store long term ECG data.

Referring back to FIG. 2, the body's surface over the sternum 26 isinherently uneven, even in children, due to the underlying bonestructure of the body of the sternum 26 and ribs 28, as well as themuscle, fat, skin, and various tissue that cover the sternum 26 andadjacent regions. The front surface of the body of the sternum 26 isslightly convex in the east-west directions and the sternum's frontsurface angles in towards the thoracic cavity from around the fourthintercostal space 27 down to the xiphoid process 24 in the north-southdirections. In the elderly, particularly in older males, the east-westconvexity can become increasingly pronounced with age, resulting in aso-called “pigeon-chested” appearance.

Conforming fit and secure adhesion to this inherently uneven surface areprovided through two interconnected structures: a flexible housing andstandoff-separated skin adhesion assembly. FIGS. 4 and 5 arerespectively side and bottom views 60, 65 of the ambulatoryelectrocardiographic monitor 41 of FIG. 3. The monitor 41 must adhere tothe sternum 26 during the monitoring period. The cover 42 and cover base44 provide a housing 61 for the monitor's electronic components. In oneembodiment, the PCB 43 is about 0.02″ thick, which allows the PCB 43 toconform to the east-west convexity of the sternum 26 and to the naturalnorth-sound inward curve towards the xiphoid process 24.

Objects adhered to the sternum 26 need to be able to both conformstatically to the shape of the chest 21 and to accommodate dynamictorsional movement, as occurs during stretching, sleeping, and otherbody movement. The PCB 43 can bend axially and laterally, but the PCB'sability to stretch is limited by physical constraints on electronicspackaging. To provide stretch, the monitor 41 utilizes a form ofindependent suspension that enables the skin adhesive layer 46 tostretch, as well as flex, independently of the housing 61. The monitor41 is adhered to the patient's skin through a layer of skin adhesive 46that is affixed to the bottom surface of the cover base 44 around theset of standoffs 45 a, 45 b. The skin adhesive layer 46 is slightlylarger than the bottom of the cover base 44 by about 0.125 in, althoughother shapes, sizes, and dimensions could be used, including shapes thatdiffer significantly from the top profile of the cover base 44. The setof electrodes 48 are removably affixed to a pair of snap-on connectorsfacing downwardly from the PCB 44 and are electronically connected tothe PCB's circuitry. Other types of connectors that allow the set ofelectrodes 48 to be removably affixed could also be used. The set ofelectrodes 48 fit within openings formed in the set of standoffs 45 a,45 b and a set of holes 66 a, 66 b, or “gel wells,” in the skin adhesivelayer 46. The electrodes 48 are coated with a conductive gel that alsoassists with adhering the monitor 41 to the patient's chest 21. Theindependent suspension is provided through the set of two or morestandoffs 46 a, 46 b that create a gap 62 of about 2.5 mm (0.1 in) toabout 6.3 mm (0.25 in) between the bottom surface of the cover base 44and the top surface of the skin adhesive layer 46. The heights of eachof the standoffs 45 a, 45 b define an increasingly wide gap between thebottom of the housing 61 and the adhesive layer 46, which permits themonitor 41 to stay securely attached to the patient 12 during torsionalmovement, such as occurs when stretching or rolling over in bed. Thestandoffs 45 a, 45 b have non-uniform heights to compensate for theunevenness of the female anatomy, as further described below withreference to FIG. 6. The gap 62 allows the housing 61 to “float” abovethe skin contact surface, while the skin adhesive layer 46 can flex andstretch along with the skin's surface on the patient's sternum chest 21.The single-point contact of each of the standoffs 45 a, 45 b thus allowsthe monitor 41 to accommodate the patient's twisting and turningmovements and remain affixed without danger of peeling off.

Breast tissue 29 (shown in FIG. 2) can increases the distance betweensensing electrodes 48 placed and the underlying heart. FIG. 6 is anexploded side view 68 of the ambulatory electrocardiographic monitor 41of FIG. 3. The degree of inward curvature of the sternum's front surfacetowards the thoracic cavity is more pronounced in women than in men. ThePCB 43 permits north-south flex of housing 61, but the amount of inwardflex may be insufficient to securely adhere the monitor 41 to an adultfemale's chest 21. To help compensate for the inward angle of the bodyof the sternum past the fourth intercostal space 27, especially inwomen, the standoffs 45 b located on the narrowest part of the monitor41 have slightly greater heights. In one embodiment, the shorterstandoffs 45 a have a height of about 2.5 mm (0.1 in) and the tallerstandoffs 45 b have a height of about 6.3 mm (0.25 in).

The electronics package of each monitor facilitates low-cost extendedwear use. FIG. 7 is a functional block diagram 70 showing the groups ofelectronic components 71 of the ambulatory electrocardiographic monitor41 of FIG. 3. The monitor 41 is self-contained and operates undermicroprogrammed control, such as described in commonly-assigned U.S.patent application, entitled “Microcontrolled ElectrocardiographicMonitoring Circuit with Feedback Control,” Ser. No. ______filed ______,pending, and U.S. patent application, entitled “MicrocontrolledElectrocardiographic Monitoring Circuit with Differential VoltageEncoding,” Ser. No. ______, filed Oct. 8, 2010, pending, the disclosuresof which are incorporated by reference. Digitally-controlled ECGmonitoring circuits provide the ability to handle the wide dynamic rangeoccasioned by the short signal vector and low signal strength affordedby a midline sternum-centered ambulatory monitoring location.

In a functional sense, the electronic components 71 can be grouped intocircuitry for a processor 72, memory 73, power supply or battery 74,data interface 75, and radio frequency identification (RFID) tag 77. Theprocessor 72 is a discrete ECG recording circuit that operates undermicroprogrammed control on a single channel of analog input signals. Tosense ECG data, the processor 72 interfaces to a set of externalelectrodes 76 through amplifiers and filters (not shown). Signalsoriginate as action potentials sensed on the skin's surface by at leastone of the electrodes 76 and a feedback signal is output through theother electrode 76. The sensed ECG data is processed into a stream ofdiscrete digital values and encoded in the persistent non-volatilememory 73, which can be implemented as electrically-erasableprogrammable read-only memory (EEPROM) or “flash” memory. The datainterface 75 enables the processor 71 to download recorded ECG data fromthe memory 73 and receive programming instructions. The processor 71,memory 72, and data interface 74 can be a single discrete integratedcircuit or a set of individual components interconnected through datachannels. The battery 74 is a conventional power cell or capacitor thatprovides power to the recording circuitry sufficient to enable extendedoperation.

In a further embodiment, either or both of the memory 73 and the battery74 can be separately provided on the skin adhesion layer 46 tofacilitate long term monitoring through use of a series of short termmonitoring periods. Space for storing recorded ECG data and power foroperating the recording circuitry are continually depleted. Providingthe memory 73 and the battery 74 on the skin adhesion layer 46 enablesthose resources to be replenished, while enabling use of the samephysical recording circuitry throughout the entire monitoring period.

The RFID tag 77 contains a unique identifier for the monitor that iseither included on the PCB 43 with the other electronic components, oris embedded into the housing 61, such as within a foam-constructed cover42. The RFID tag 77 is used during monitoring to pair a monitor 41 to atracking number that can be used by the patient 12, referral center, andphysician or staff to track the physical whereabouts of the monitor 41and to determine the post-monitoring status of diagnosis and follow upcare. The RFID tag 77 is self-powered or can be powered through thebattery 74. The RFID tag 77 is accessed using standard RFID transmitterand receiver units. Other components in addition to or in lieu of theelectronic components 71 are possible, such as used to record additionaltypes of patient physiometry or to provide further onboard capabilities.

In a further embodiment, the electronic components 71 also include anactimetry sensor 78 to measure gross motor activity undertaken by thepatient, such as through walking, running, changing posture or sleepposition, and other body motions. For instance, the actimetry sensor 78may record movement, which indicates that the patient was climbingstairs at the same time that an increase in heart rate was recorded bythe monitor 11. Particularly, when actigraphy is combined with thepatient's subjective impressions as contemporaneously recorded in hisdiary, the physician can confirm or better understand hemodynamicchanges and other aspects of cardiac physiology as reflected in therecorded ECG data.

The monitor 41 may be fully or partially disposable. For instance, theelectronic components 71 on the PCB 43 may be refurbished and recycledfor multiple uses, while the housing 61 and skin adhesive 46 would bedisposed after a single use. During refurbishment, the battery 74 wouldbe replaced and the memory 73 wiped clean. Alternatively, the entiremonitor 41 may be used only once, followed by appropriate disposal.

While the invention has been particularly shown and described asreferenced to the embodiments thereof, those skilled in the art willunderstand that the foregoing and other changes in form and detail maybe made therein without departing from the spirit and scope.

1. A method for performing ambulatory electrocardiographic (ECG)monitoring on an adult female, comprising: provisioning an ambulatoryECG monitor comprising a plurality of sensing electrodes coupled toself-powered sensing circuitry; locating a monitoring site on thesurface of a patient's chest at midline and above the body of thesternum adjacent to the fourth and fifth intercostal spaces between thebreasts in the upper portion of the intermammary cleft; aligning andplacing the electrodes along the midline; evaluating interference frombreast tissue with placement of the ambulatory monitor at the monitoringsite; removably adhering the ambulatory ECG monitor to the monitoringsite clear of any breast tissue interference for the duration ofmonitoring; and sensing ECG data through the sensing electrodes at themonitoring site and recording the sensed ECG data into the sensingcircuitry.
 2. A method according to claim 1, further comprising:selecting a circuit board exhibiting axial and lateral flexibility;provisioning the sensing circuitry on the selected circuit board andenclosing the sensing circuitry within a housing; and conformablyflexing the circuit board within the housing along the contours of thechest's surface.
 3. A method according to claim 1, further comprising:enclosing the sensing circuitry within a housing; selecting a layer ofskin adhesive and a set of standoffs comprised of non-uniform heightswith the standoffs comprised of greater height located closer to thexiphoid process of the patient than the standoffs comprised of lesserheight; attaching the skin adhesive layer to a bottom surface of thehousing separated by the set of standoffs; and conformably adhering theskin adhesive layer to the chest's surface with the housing separatedfrom the chest's surface by a gap formed by the heights of the set ofstandoffs.
 4. A method according to claim 3, further comprising one ofdefining the skin adhesive layer in a shape comparable to the shape ofthe bottom of the housing; and defining the skin adhesive layer in ashape differing from the shape of the bottom of the housing.
 5. A methodaccording to claim 1, further comprising: fashioning a housing comprisedof an elongated triangular shape with rounded vertices; and enclosingthe sensing circuitry within a housing, wherein the housing is removablyadhered to the monitoring site with the narrowest part of the triangularshape facing towards the patient's feet.
 6. A method for performingambulatory electrocardiographic (ECG) monitoring at a midlinesternum-centered location of an adult female, comprising: provisioningan ambulatory ECG monitor comprising a plurality of sensing electrodescoupled to self-powered sensing circuitry and enclosed in a flexiblehousing; independently suspending a layer of skin adhesive from a bottomof the flexible housing; locating a monitoring site on the surface of apatient's chest at midline and above the body of the sternum adjacent tothe fourth and fifth intercostal spaces between the breasts in the upperportion of the intermammary cleft; evaluating interference from breasttissue with placement of the ambulatory monitor at the monitoring site;conformably placing the ambulatory ECG monitor, comprising: aligning andplacing the electrodes along the midline; removably adhering the skinadhesive to the monitoring site for the duration of monitoring;positioning the housing to avoid the breast tissue interference; andbending the housing axially and laterally along the contours of themonitoring site; and sensing ECG data through the sensing electrodes atthe monitoring site and recording the sensed ECG data into the sensingcircuitry.
 7. A method according to claim 6, further comprising:identifying the breast tissue interference by evaluating each of width,length, depth, and relative location of the adult female patient'sintermammary cleft based on one or more of breast size, shape, position,symmetry, overall body physique, posture, type and fit of brassiereworn, and presence of artificial breast implants relative to the size ofthe flexible housing.
 8. A method according to claim 6, furthercomprising: providing a set of standoffs between the skin adhesive layerand the bottom surface of the housing, the standoffs comprised ofnon-uniform heights with the standoffs comprised of greater heightaffixed at opposite ends of the bottom surface of the housing than thestandoffs comprised of lesser height; and permitting the skin adhesivelayer to flex and stretch in conformity with the patient's skin at themonitoring site.
 9. A method according to claim 6, further comprisingone of: defining the skin adhesive layer in a shape comparable to theshape of the bottom of the housing; and defining the skin adhesive layerin a shape differing from the shape of the bottom of the housing.
 10. Anambulatory electrocardiographic (ECG) monitor for an adult woman,comprising: self-powered ECG sensing circuitry; a plurality of sensingelectrodes coupled to the sensing circuitry; a housing enclosing thesensing circuitry; and a skin adhesive layer facing a contact surfaceand independently suspended from the housing with a set of standoffshaving non-uniform heights affixed to and defining an increasingly widegap between the skin adhesive layer and a bottom surface of the housing.11. A monitor according to claim 10, further comprising: a circuit boardexhibiting axial and lateral flexibility and upon which the sensingcircuitry is comprised.
 12. A monitor according to claim 10, wherein oneor more cutouts are defined around the periphery of the skin adhesive.13. A monitor according to claim 10, wherein the skin adhesive layercomprises adhesive fabric, cloth, foam, and latex.
 14. A monitoraccording to claim 10, wherein the skin adhesive layer is defined in ashape comparable to one of the shape of the bottom of the housing and ashape differing from the shape of the bottom of the housing.
 15. Amonitor according to claim 10, wherein the sensing circuitry compensatesfor gaps in recording of ECG data resulting from disconnection andreconnection of the sensing electrodes.
 16. A monitor according to claim10, wherein the housing is unshielded.
 17. An ambulatoryelectrocardiographic (ECG) monitor with conformal shape and independentsuspension for an adult woman, comprising: a flexible ECG circuitrybody, comprising: self-powered ECG sensing circuitry comprising aprocessor, memory, and finite power supply; a circuit board exhibitingaxial and lateral flexibility and upon which the sensing circuitry iscomprised; and a housing enclosing the circuit board; a plurality ofsensing electrodes coupled to the processor, which processes and storessensed ECG data into the memory; and a skin adhesion assembly,comprising: a layer of skin adhesive facing a contact surface; and a setof standoffs having non-uniform heights affixed to and defining anincreasingly wide gap between the skin adhesive layer and a bottomsurface of the housing of the circuitry body.
 18. A monitor according toclaim 17, further comprising: a hole defined through a center of each ofthe standoffs, wherein the sensing electrodes are positioned in each ofthe holes facing the contact surface.
 19. A monitor according to claim17, wherein one or more cutouts are defined around the periphery of theskin adhesive.
 20. A monitor according to claim 17, further comprising:a radio frequency identification tag comprised with the flexible ECGcircuitry body and providing a unique identifier.
 21. A monitoraccording to claim 17, further comprising: an actimetry sensor coupledwith the sensing circuitry and storing gross motor activity data intothe memory.
 22. A monitor according to claim 17, wherein at least one ofthe memory and the finite power supply are comprised on the skinadhesive layer instead of the circuitry body.
 23. A monitor according toclaim 17, the skin adhesive layer comprises adhesive fabric, cloth,foam, and latex.
 24. A monitor according to claim 17, wherein the skinadhesive layer is defined in a shape comparable to one of the shape ofthe bottom of the housing and a shape differing from the shape of thebottom of the housing.
 25. A monitor according to claim 17, wherein theplurality of electrodes are spaced less than 6 cm apart.
 26. A monitoraccording to claim 17, wherein the monitor weighs not more than 28 g(1.0 oz).